A quadrature coil system of this kind in known from EP-B 71 896. It can be used for receiving spin resonance signals and/or for generating high-frequency magnetic fields. In the receiving mode, the signal-to-noise ratio can be improved by up to 3 dB with respect to reception utilizing only one of these coils. In the transmission mode, circularly polarized magnetic high-frequency fields can be generated by supplying the two high-frequency coils with high-frequency currents whose phase has been shifted 90.degree. with respect to one another, so that the required transmission power is halved.
The two high-frequency coil systems of the known system are formed by saddle-shaped coils which have been rotated through 90.degree. with respect to one another, so that their field directions (i.e. the direction of the magnetic fields to be generated thereby or the direction of a high-frequency magnetic field in which the voltage induced in the coil has a maximum) also enclose an angle of 90.degree.. The saddle-shaped coils are arranged on the surfaces of a cylindrical support and generate magnetic fields which extend perpendicular to the symmetry axis. The steady, uniform magnetic field which is generated in the magnetic resonance examination apparatus and which is a prerequisite for examinations based on magnetic resonance must then extend perpendicular to the field directions of the two saddle-shaped coils, i.e. in the direction of the symmetry axis. Because this symmetry axis must be coincident with the longitudinal axis of a patient being examined, the magnetic field must extend in the direction of the longitudinal axis of the patient.
However, also known are magnetic resonance examination apparatus in which the steady magnetic field extends perpendicularly to the longitudinal axis of the patient. A suitable examination apparatus in this respect is described in a prior German Patent Application P 39 18 743.8. It comprises two similar coil systems, each of which comprises several mutually offset, annular conductor loops which are merely inductively coupled to one another. The conductor loops are situated in planes which intersect at right angles and which extend at an angle of approximately 45.degree. with respect to the longitudinal axis of the patient's body. Therefore, a quadrature coil system of this kind is suitable only for performing examinations of the head or the extremities.